I've been messing with this since it came out. I used to own Trainz 2004 on the PC and have some experience with this program. I'm really amazed that they managed to port this program to the iPad, since it is just packed with features. Most people who aren't train enthusiasts will pass this over quickly since on the surface it seems very boring ("meh... you just drive a train around??"). What they might not realize is you can CREATE layouts from scratch... mountains, valleys, textures, roads, houses, junctions... the list goes on and on. So essentially this is a "train driving" program coupled with an extensively-featured 3D modeling program, the likes of which I have never seen on the iPad before. It is a very unique app.
What's most startling is that they packed this into an iPad and it runs surprisingly well with only 256 mb of RAM. I've spent many hours using this already and it hasn't crashed ONCE. And this is Version 1. That is truly amazing.
Now, the bad news is the UI is not completely intuitive or fully optimized for the iPad. This is one complicated app. On the surface it is pretty easy to click around, but given the amount of control they give you, there are a LOT of buttons. It takes certain types of gestures to do things like place rails and set gradients, and none of this is explained or obvious. Took me a lot of trial and error to figure it out. There is no manual. Supposedly they are working on it. Thankfully there is an UNDO button. I've used it a lot.
I don't want to beat them up too much. It's clear they put a lot of thought into the UI for the PC, and in many ways it is elegant. But the port to the iPad still needs work and it really needs some training videos on Youtube or something.
That said, it's amazing what you can do. I created this mountain layout entirely from scratch. I shaped every mountain, placed every tree, laid every track, and painted every texture. This is just scratching the surface of the library of objects you can choose from. None of it is cookie-cutter. It's all user-controlled. Heck, even if you aren't into trains, if you like creating cities or nature scenes or whatever, you can get totally engrossed in this app. Once you get past the frustration of learning the UI, that is.